南海北部陆架晚第三纪δ~(13)C记录与古生产力——以珠江口盆地BY7-1-1和PY33-1-1井为例

南海珠江口盆地ＢＹ７－１－１及ＰＹ３３－１－１井晚第三纪浮游有孔虫的丰度、底栖有孔虫小泡虫超科中葡萄虫（Ｕｖｉｇｅｒｉｎａ）和小泡虫（Ｂｕｌｉｍｉｎａ）的相对丰度（Ｕ＋Ｂ含量）以及浮游有孔虫壳体的δ１３Ｃ记录表明，晚第三纪期间表层水生产力总体上呈增高趋势，其中早中新世为表层水生产力较低的时期，但由Ｎ４至Ｎ８带表现为递增趋势，中—晚中新世为高生产力时期，早上新世为又一个高生产力时期。其中中—晚中新世时期本区最可能处于非上升流的高生产力地区，而早上新世为受上升流影响的高生产力地区。     

南海深海沉积中的更新统/上新统界线及与意大利Vrica层型剖面的对比

应用浮游有孔虫定量统计、底栖有孔虫氧同位素和磁性地层学等资料来确定南海ODP1148站深海沉积中的上新统／更新统(P／P)界线。氧同位素期(MIS)64和65之间的P／P界线在1148站位于井深112．75m处，计算年龄为1．805Ma，在地层对比上与Vrica层型剖面的P／P界线一致。浮游有孔虫Pulleniatina obliquiloculata在MIS62出现以右旋壳为主的转变，计算年龄为1．76Ma，此事件和Olduvai极性亚时顶界看来是最接近P／P界线的可靠时间面。除此以外，在1148站P／P界线及其附近没有发现重大的地层学和环境变化事件。相比之下，1148站底栖δ^18O值在3．05～2．53Ma期间快速变重，冬季表层海水温度下降了5℃，指示了北半球冰盖的形成。     

渐新世/中新世分界的地层学事件

介绍渐新世/中新世分界面(即古近纪/新近纪分界面)附近的浮游有孔虫和钙质超微化石事件及其新年龄。2004年国际地层年代表确定该分界面位于第58长偏心率周期弱振幅处,古地磁事件C6Cn.2n底面,经天文调谐后的年龄为23.03 Ma。发生在该界面附近的生物地层学事件主要是浮游有孔虫Paragloborotalia kugleri的始现面(22.96 Ma)和钙质超微化石Sphenolithus delphix的末现面(23.11 Ma)。在南海北部东沙群岛附近的大洋钻探ODP1148站,渐新世/中新世界面以崩塌沉积物为特征,有明显沉积间断,标志南海当时有较大范围的构造运动。     

南海表层沉积钙质超微化石氧碳同位素研究

对南海34个站位表层沉积中的钙质超微化石进行了氧碳稳定同位素分析.结果表明,钙质超微化石δ^18O化范围为-2.656‰～0.006‰,平均为-1.517‰;δ13C值变化范围为-1.510‰～0.778‰,平均为0.140‰.通过与有孔虫同位素分析结果相比较,发现钙质超微化石δ^18O高于浮游有孔虫而低于底栖有孔虫,δ13C值低于浮游有孔虫而高于底栖有孔虫.从平面分布来看,南海表层沉积钙质超微化石氧同位素在东北和西南各存在一个小于-1.5‰的低值区,碳同位素在东北存在一个小于0的低值区.钙质超微化石与有孔虫同位素值的差异性可能与其生命效应及生活环境有关.而钙质超微化石与有孔虫同位素平面分布规律上的不同也揭示了海水温度、盐度、营养水平等海洋参数可能对超微化石和有孔虫同位素的分馏起不同控制作用.     

16Ma以来南海北部海域古水温变化规律与机制

长期以来古海洋表层古水温研究的热点主要集中在第四纪,很少涉及到2.5Ma之前。利用ODP 184航次1147和1148站位的获得的相关资料,并主要采用长链烯酮U3k7)和底栖有孔虫氧同位素(δ18 O)两种方法,计算海水氧同位素组成,然后,利用浮游有孔虫氧同位素法计算16Ma以来的海水温度变化,探讨南海北部16Ma以来的古海水温度变化机制。结果表明,南海北部水温总体趋势与全球气候发展相对应,在北半球冰盖形成时期,海水表层温度与代表高纬冰盖体积大小的底栖有孔虫δ18 O几乎同步变化,反映出南海热带海区古气候变化的特殊性,为进一步研究低纬热带海区在全球古气候变化中的作用提供了新证据。     

南海北部陆架晚第三纪δ^13C记录与古生产力

南海经珠江口盆地ＢＹ７－１－１及ＰＹ３３－１－１井晚第三服游有孔虫的丰度、底栖有孔虫小虫超科中葡萄虫和小虫和相对丰度以及浮游有孔虫壳体的δ＾１３Ｃ记录表明，晚第三纪期间表层以水生产力总体上呈增高趋势，其中早中民为表层水生产力较低的时期但由Ｎ４至Ｎ８带表现为递增趋势，中一晚中新世为高生产力晚期，早上新世为又一个高生产力时期。中－晚世时期本区最可能处于非上升流的高生产力地区，而早上新世为受上升流影响的     

更新世冰期的全球深海绝灭事件

据估计 ,深海有孔虫种的交替速率为２ %／Ｍａ ,比新生代浅水底栖（５ %／Ｍａ）或者浮游有孔虫（１１ %／Ｍａ）明显偏低。白垩纪—第三纪边界（６５Ｍａ）或附近的事件引发了陆地和浅水以及部分半远洋生物的灾难性绝灭 ,但是对深海底栖有孔虫的影响很小。大部分深海有孔虫绝灭（３０ %～５０ %的种消失了）出现于晚古新世冰后高温期（ＬＰＴＭ ,５５Ｍａ） ,它起因于贫氧、温暖的侵蚀性底层水以及同时发生的表层生产力的变化。晚始新世至早渐新世（３６～３０Ｍａ）和中中新世也发现了深海底栖有孔虫的种类交替增强有全球蔓延的趋势。对中…     

中更新世气候转型期西太平洋暖池的表层海水温度和氧同位素变化

通过对大洋钻探(ODP)第130航次807站A孔井深12.54～16.38m沉积物中浮游和底栖有孔虫的稳定同位素δ18 O以及浮游有孔虫壳体的Mg/Ca测试,揭示了中更新世气候转型期(800～1 000kaBP)西太平洋暖池表层海水温度和氧同位素的变化。研究发现,中更新世时期ODP 807站的表层海水温度在25.1～30.9℃之间浮动,平均为28.4℃,接近现代暖池区实测温度值,冰期/间冰期之间的温度差值在1.5～5℃左右,与晚第四纪时的温差相近;同时,表层海水温度和底栖有孔虫氧同位素呈现同步变化的趋势,没有明显的超前或滞后的相位关系,区别于前人在暖池区的研究结果。间冰期时,表层海水温度上升伴随着温跃层变深、盐度降低,与现代西太平洋暖池La Ni珘na状态类似;冰期时则类似于El Ni珘no状态。中更新世气候转型期,西太平洋暖池的表层海水温度、温跃层深度变化受低纬热带驱动影响,都显示出强烈的岁差周期(16.8ka),而底层水氧同位素更多受到高纬的影响。     

南海东北部晚第四纪古生产力变化

通过对南海东北部、吕宋岛西北岩外１７９２８柱状样吕浮游、底栖有孔虫丰度及其与生产力有关和属种含量变化的研究,发现该柱状样在末次冰期（氧同位素２～４期）和氧同位素６期时,浮游、底栖有孔虫丰度增高,高生产力的有孔虫含量也在这两个时期出现高值,说明此时该区具有同的生力水平,这种现象可能与冰期时陆营养盐输入量增加、东亚冬季风增强并在此形成上升流有关。     

南海北部ODP1148站中新世以来的碳酸盐含量变化及其古环境意义

对南海北部 ODP 114 8站采自孔深 4 6 5 m以上的 170 0个沉积物样品 ,测定了 Ca CO3含量、Ca CO3堆积速率、非钙质堆积速率、浮游有孔虫丰度、粗组分百分含量 (>6 3μm)、浮游有孔虫破壳率和底栖有孔虫在有孔虫全群中的百分含量。碳酸盐百分含量和碳酸盐堆积速率自 2 4 Ma以来的变化呈现逐步下降的趋势 ,但在 2 4 .0～ 15 .8、14 .2～ 11.6、10 .6～ 4 .8和 3.4～ 0 Ma四个时期具有高碳酸盐生产力 ,其中 10 .6～ 4 .8Ma的高生产力与印度洋和太平洋中新世晚期和上新世早期的“生物勃发”相对应。非钙质和碳酸盐两者堆积速率变化趋势在总体上相似 ,反映了陆源物质输入对碳酸盐生产力的影响。 3.4 Ma后非钙质堆积速率的大幅度增长主要与青藏高原和台湾岛的隆起有关 ,它们也是上新世晚期和第四纪 Ca CO3百分含量显著下降的主要原因。 2 4 Ma以来南海北部碳酸盐的保存逐渐变弱 ,而碳酸盐溶解作用逐渐增强 ,在 15 .8～ 14 .2、11.6～ 10 .6和 4 .8～ 3.4 Ma存在 3个显著的碳酸盐溶解事件 ,其中 11.6～ 10 .6 Ma的溶解事件与赤道太平洋和加勒比海的中—晚中新世“碳酸盐崩溃”事件相当 ,说明该事件具更广泛的全球影响     

Chemostratigraphic documentation of a complete Miocene intermediate-depth section in the Southern Ocean: Ocean Drilling Program Site 1120, Campbell Plateau off New Zealand

An integrated chemostratigraphic (⁸⁷Sr/⁸⁶Sr, δ¹³C and δ¹⁸O) study of benthic foraminifera is presented for a 210 m-thick, intermediate depth (upper/middle bathyal transition), Miocene nannofossil ooze section of Ocean Drilling Program Site 1120, Campbell Plateau off New Zealand. Our results indicate that new ⁸⁷Sr/⁸⁶Sr, δ¹³C and δ¹⁸O profiles are wholly consistent with their respective Miocene reference curves. These observations facilitate identification of a total of five reliable chemostratigraphic datums, which are based on the fundamental structural changes in the ⁸⁷Sr/⁸⁶Sr curve and paired simultaneous δ¹³C and δ¹⁸O events. The resultant age–depth relationship clearly shows that the Miocene (20–5 Ma) biopelagic sedimentation on the Campbell Plateau was essentially continuous at a moderate to high, linear sedimentation rate (17.5 m/m.y. with an exception of the uppermost 13 m). Our findings do not support the shipboard biostratigraphic age model, which assumes that the critical early–middle Miocene transition was interrupted by a major hiatus (<~3 m.y.). Because of its unique bathymetric setting at a paleowater-depth of ~ 600 m, which is among the shallowest of the coeval isotopically studied deep-sea sections in the South Pacific/Southern Ocean, Site 1120 will serve as a reference section for surveying the evolution of intermediate-water paleoceanography in the Southern Hemisphere across the middle Miocene climatic transition.     

Biomarkers reveal the terrigenous organic matter enrichment in the late Oligocene-early Miocene marine shales in the Ying-Qiong Basin,South China Sea

The increase of total organic carbon content of the late Oligocene-early Miocene terrigenously-dominated marine shales in the shallower depth intervals was reported in the Ying-Qiong Basin, South China Sea. The organic enriched lower Sanya Formation shales(early Miocene) have biomarker characteristics of tropical/subtropical plants, with abundant high molecular weight n-alkanes, angiosperm-derived oleanane,rearranged oleananes Ⅰ, Ⅱ, Ⅱ, tricyclic/tetracyclic terpanes including des-A-oleanane, X, ...     

Late Miocene stable isotope stratigraphy of SE Atlantic ODP Site 1085: Relation to Messinian events

High-resolution benthic oxygen isotope and XRF (Fe and Ca) records from Site 1085 drilled in the Mid-Cape basin (ODP Leg 175) are used to investigate global climate changes during the Late Miocene in relation to Messinian geological events. The cyclic fluctuations of the time series at Site 1085 enable us to establish a reliable chronology for the time interval 7.3–4.7 Ma. Spectral analysis of the δ¹⁸O record indicates that the 41-kyr period of orbital obliquity dominates the Late Miocene record. A global climate record was extracted from the oxygen isotopic composition of benthic foraminifera. Both long- and short-term variabilities in the climate record are discussed in terms of sea-level and deep-water temperature changes. The time interval 7.3–6.25 Ma characterized by low-amplitude δ¹⁸O variations is followed by a period marked by maximum in the δ¹⁸O values (6.25–5.57 Ma). At about 5.56 Ma, a rapid decrease in δ¹⁸O values is documented that may reflect a warming of deep-water temperature associated with a global warming period. Comparison between the timing of the oceanic isotope events and the chronology of the Mediterranean Salinity Crisis suggest that global eustatic processes were not essential in the Mediterranean Salinity Crisis history. From our data, we infer that the global warmth documented in the Early/mid-Pliocene probably started during the Late Miocene (at 5.55 Ma). At the same time, the onset of evaporite deposition in the central basin of the Mediterranean Sea took place. Sharp changes in the sedimentation rates, mainly driven by terrigenous input at this site, are observed during the Messinian Stage.     

Observations of contrasted glacial-interglacial dissolution of foraminifera above the lysocline in the Bay of Bengal,northeastern Indian Ocean

Site U1446 (19°50’N, 85°44’E, at water depth 1 430 m) was drilled during Expedition 353 (Indian monsoon rainfall) of the International Ocean Discovery Program (IODP). It is located in the Mahanadi offshore basin, on the northern Bay of Bengal. Sedimentation rates and contents of biocarbonates are high at this relatively shallow site. Using a micropaleontological approach, we examined planktonic and benthic foraminifera in the upper around 40 m of this site, spanning the last around 190 ka. A striking feature of the foraminiferal record is the occurrence of strong but varying dissolution although the site is located well above the modern lysocline. Such strong dissolution has never been reported in this area. We estimated the flux of foraminifera and quantified the ratio of benthic foraminifera over total foraminifera (benthic/total foraminifera) along with the foraminifer fragmentation index in order to characterize past changes in this above-lysocline dissolution. This study reveals a clear glacial-interglacial contrast, with a stronger dissolution during marine isotope stages (MISs) 1 and 5 than during MISs 2–4 and 6. Such a difference in preservation is likely to have a strong impact on geochemical proxies measured on foraminifera. Our new observations call for an in-depth study of the causes of such above-lysocline dissolution in the region, and an evaluation of its impact on the foraminifera-based proxies used for paleoenvironmental reconstruction.     

A 33 Ma lithostratigraphic record of tectonic and paleoceanographic evolution of the South China Sea

The 853 m thick sediment sequence recovered at ODP Site 1148 provides an unprecedented record of tectonic and paleoceanographic evolution in the South China Sea over the past 33 Ma. Litho-, bio-, and chemo-stratigraphic studies helped identify six periods of changes marking the major steps of the South China Sea geohistory. Rapid deposition with sedimentation rates of 60 m/Ma or more characterized the early Oligocene rifting. Several unconformities from the slumped unit between 457 and 495 mcd together erased about 3 Ma late Oligocene record, providing solid evidence of tectonic transition from rifting/slow spreading to rapid spreading in the South China Sea. Slow sedimentation of 20–30 m/Ma signifies stable seafloor spreading in the early Miocene. Dissolution may have affected the completeness of Miocene–Pleistocene succession with short-term hiatuses beyond current biostratigraphical resolution. Five major dissolution events, D-1 to D-5, characterize the stepwise development of deep water masses in close association to post-Oligocene South China Sea basin transformation. The concurrence of local and global dissolution events in the Miocene and Pliocene suggests climatic forcing as the main mechanism causing deep water circulation changes concomitantly in world oceans and in marginal seas. A return of high sedimentation rate of 60 m/Ma to the late Pliocene and Pleistocene South China Sea was caused by intensified down-slope transport due to frequent sea level fluctuations and exposure of a large shelf area during sea level low-stands. The six paleoceanographic stages, respectively corresponding to rifting (33–28.5 Ma), changing spreading southward (28.5–23 Ma), stable spreading to end of spreading (23–15 Ma), post-spreading balance (15–9 Ma), further modification and monsoon influence (9–5 Ma), and glacial prevalence (5–0 Ma), had transformed the South China Sea from a series of deep grabens to a rapidly expanding open gulf and finally to a semi-enclosed marginal sea in the past 33 Ma.     

Sedimentary and structural evolution of the Eastern South Korea Plateau (ESKP), East Sea (Japan Sea)

The East Sea (Japan Sea) is a semi-enclosed back-arc basin that is thought to preserve a significant record of tectonic evolution and paleo-climatic changes of Eastern Asia during the Neogene. We use here 2-D regional multi-channel seismic reflection profiles and borehole data from Expedition 346 of the Integrated Ocean Drilling Program (IODP) to provide new constraints on the geological history of the Eastern South Korea Plateau (ESKP). The ESKP represents a structurally-complex basement high in the southwestern East Sea which formed during rifting of the back-arc basin. Our new observations show that the ESKP is composed of numerous horsts and grabens controlled by NE-trending normal faults. The acoustic basement is blanketed by Oligocene to recent sediments that have preferentially accumulated in topographic lows (up to 1.5 km thick) and have been cored during Expedition 346 at Site U1430 close to the southern margin of the ESKP. Seismic profiles in the ESKP reveal three units separated by regional unconformities. These seismic units closely correspond to IODP lithostratigraphic units defined at Site U1430, where biostratigraphic data can be used to constrain the timing of three main evolutionary stages of the ESKP. Stage 1 was related to rifting in the late Oligocene and middle Miocene, terminated by a regional uplift leading to an erosional phase in the middle Miocene. Stage 2 was associated with subsidence in the middle and late Miocene and uplift and accompanying erosion or non-deposition in the latest late Miocene. Stage 3 (Pliocene to present) recorded overall uniform hemipelagic-pelagic subsidence of the ESKP with short-lived tectonically-induced uplifts in the late middle Miocene and latest Miocene-early Pliocene. The three stages of evolution of the ESKP closely correlate to sedimentary changes since the Oligocene and suggest a direct control of regional/local tectonics on sedimentation patterns in the southwestern East Sea, with secondary influence of regional climatic and paleo-oceanographic processes.     

崂山湾潮间带食物网结构的碳稳定同位素初步研究

通过对1993年8月和1994年2和5月在崂山湾潮间带采集的底栖生物碳稳定同位素组成(δ13C值)的分析,发现该区底栖动物的主要食物来源以δ13C值大致可划分为4类:水体中的颗粒有机质(POM)、底栖硅藻、大型底栖藻类和底泥中的有机物质(SOM).研究结果表明,底栖动物的碳稳定同位素组成与其所摄食的食物的碳稳定同位素组成有密切的关系,因此,底栖动物的碳稳定同位素组成可以用于研究其食物来源.碳稳定同位素数据证实,双壳类等滤食性动物的食物来源主要是POM;甲壳动物的δ13C值的范围较大,证明其食物来源的多样性;底栖硅藻是多数腹足类食物来源的相当重要组成部分.用碳稳定同位素示踪剂对该区底栖-水体耦合作用的初步研究表明,水体中的POM是底栖动物的重要食物来源,但底泥中有机质和底栖硅藻也是许多底栖动物食物来源的相当重要的组成部分.     

Tectonostratigraphic evolution of the Morichito piggyback basin, Eastern Venezuelan Basin

The Morichito piggyback basin (MPB) is a SW-NE-oriented depocenter in the Eastern Venezuelan Foreland Basin (EVFB). This piggyback basin formed by overlying the Pirital thrust during the middle to late Miocene as a result of oblique collision between the Caribbean and South-American Plates. The MPB covers an area encompassing approximately 1000 km² between the Serrania del Interior range and the Pirital high, which is a hanging wall uplift along the Pirital thrust that acts as a confining barrier on the southern boundary of the MPB. Previous studies have tried to address the tectonostratigraphic significance of the MPB, but new biostratigraphic information and recently acquired 3D seismic data have allowed us to expand the understanding of this basin. The MPB occupies a relatively small area of the EVFB; however, the MPB contains a valuable stratigraphic record that can be used to unveil the timing of the main deformational events that took place in the EVFB.This work presents the tectonostratigraphic evolution of the MPB by defining four tectonostratigraphic sequences (T1-T4). Each sequence was defined on the basis of integration of well logs, biostratigraphy, and seismic geomorphological interpretations. T1 (24-16 Ma) (late Oligocene to middle Miocene), which was deposited in shallow-marine environments, extends to the south of the Pirital high beyond the boundaries of the MPB. T1 is equivalent to the early foredeep stage of the EVFB, having been formed when structural deformation and uplifting were already occurring to the north on the proto-Serrania del Interior range (∼24-16 Ma) and the Pirital thrust was active (∼22 Ma). T2 (16-11 Ma) (middle to late Miocene) is composed of alluvial-fan deposits derived from the proto-Serrania del Interior range. The geometry and internal configuration of T2 indicate that during this time the basin was transitioning from an open-foreland basin to a confined piggyback basin. During deposition of T2, the Pirital fault was active as an out-of-sequence thrusting event (16-∼11 ma). T3 (late Miocene) and T4 (early Pliocene to Recent), composed of shallow-marine and fluvial deposits, were deposited in an already restricted piggyback basin. The Pirital high was already in place during deposition of T3 (∼11-9.3 ma). T3 and T4 represent the final phases of MPB infilling, when tectonic activity and subsidence were at their lowest rates. MPB sedimentary infilling dates the activity of thrusting events in the proto-Serrania del Interior (∼24-16 Ma), timing of maximum deformation associated with the Pirital out-of-sequence thrusting event (16-∼11 Ma), timing of final emplacement of the Pirital high (∼11-9.3 Ma), and the beginning of tectonic quiescence (<5.2 Ma).     

A preliminary study on benthos food web structure of tidal zone in the Laoshan Bay by using stable carbon isotopes

By analyses of carbon isotopic composition(δ¹³C values) of the benthos collected in the Laoshan Bay in August 1993 and February and May 1994, it is found that the main food sources of the benthos can be divided into four groups in terms of carbon isotope composition: Particulate Organic Matter (POM),benthic diatoms, benthic macroalgae and the organic matter in sediments.The results show that the carbon isotopic composition of the benthic animals has a close relation with that of the food they take in.The carbon isotopic compositions of benthos may be useful in elucidating their food sources.The carbon isotopic data have confirmed that POM is the main food source of the benthic filter feeders such as bivalves; crustaceans have a wide range of δ¹³C values, showing their food source has diversity; benthic diatoms are an important fraction of the food for most of gastropods.A preliminary investigation of the benthic-pelagic coupling in that region using the stable carbon isotopic tracers has confirmed the importance of POM as a food source for benthos in this region,but the organic matter in sediments and benthic diatoms are also relatively important for a lot of benthic animals.The benthic-pelagic coupling in the Laoshan Bay temperate ecosystem is not so tight as that in ecosystems at higher latitudes such as north-eastern water polynya.